272 Mr. R. P. Greg on the Periodicity of the Solar Spots, 



do not agree — in fact rather the reverse — with the nearest periods 

 of spot-maximum ; e. g. Jupiter was in perihelion in 

 July 1809-| fl816^ 



Feb. 1845 1 ] 1848 f maxima ' 



Dec. 1856 J LI860J 



There are then certainly considerable difficulties in the way of 

 accounting for the spot-period of 11*1 years, if we suppose that 

 Jupiter's sidereal period of 11*8 years necessarily regulates it. 



Being, however, strongly convinced in my own mind that pla- 

 netary influences would necessarily have some effect, one way if 

 not in another, upon the sun's physical constitution, and pro- 

 bably influence the phenomenon of periodicity in spot-maximum 

 and minimum, I requested a person of my acquaintance, natu- 

 rally endowed with a mathematical and astronomical turn of 

 mind, to see if he could not find some synodical period answer- 

 ing to the secular term of 11*1 years. I advised him, in the 

 first place, to investigate the period of Jupiter, and his conjunc- 

 tions with Saturn, the Earth, and Venus ; in the second place, 

 to take likewise into especial consideration their positions in their 

 own orbits as regards least distance from the sun, and the times 

 when they were in line with the sun's equator. He says in 

 reply, in one of his letters to me, "I have failed in finding 

 out some configuration of the planets to account for the spot- 

 cycle of 11*1 years; I can find nothing that comes at all near 

 it, but the return of Jupiter to the same point in his orbit once 

 in about 12 years; and this epoch is without any certainty of 

 either conjunction or opposition with any of the other planets. 

 Jupiter passes Saturn at periods of about 20 years, and Uranus 

 at periods of about 14| years; and he is passed by the smaller 

 planets at much shorter periods than 11 years. And it does not 

 appear that this particular point in the orbit of Jupiter, where 

 he is situated at the time of spot-maximum, is either the peri- 

 helion, aphelion, or either of his nodes. The perihelion of Jupiter 

 is in Aries, and he was last in that point (the nearest point to the 

 sun) about December 1856; and as the line of apsides moves 

 very slowly, he will return to the same point again in 1869, and 

 so on every 12 years for many returns." 



On the 9th of September last I received from him the following 

 letter, which I give verbatim, as being, at least, curious and 

 interesting : — 



"Dear Sir, — In searching for the solar-spots cycle, in some 

 arrangement of the planets, I hit upon a rather remarkable con- 

 junction, which is as follows : — 



u Supposing the sun to make one revolution on his axis in 25 



